The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Aspects of the present invention relate to a direct-drive wind turbine comprising a tower with a nacelle, said nacelle being provided with a direct-drive generator and a rotatable hub carrying turbine blades, wherein the direct-drive generator comprises an outer stator and an inner rotor and has a first side facing the turbine blades and a second side facing away from the turbine blades, the nacelle further being provided with a slip ring for transferring power and/or signals from the nacelle to the rotatable hub, said slip ring being mounted coaxially with the centerline of the direct-drive generator.
A hub carrying turbine blades requires power, for example for powering pitch motors, various sensors (such as sensors measuring the pitch of a turbine blade), etc. This requires one or more electrical connections between the stationary world (the tower with the nacelle) and the rotatable hub. This function is performed by a slip ring. For direct-drive generators, access to the hub is provided via the hollow center of the generator, or via a bypass. The latter is inconvenient because it is dangerous for maintenance personal and adds significant additional cost. The first option is problematic for those direct-drive generators that have an inner rotor, as a result of which the inside wall of the direct-drive generator is not part of the stationary world. This is in particular the case for direct-drive turbines that have bearings at both the first and the second end of the direct-drive generator. More specifically the problem is that the placement of the slip ring at the second end would block the passage through the direct-drive generator, and placement of the slip ring at the first end requires a long frame extending through the hollow axis of direct-drive generator, which is a burden in view of the required co-axial placement of the slip ring. Such a frame would have to be very rigid, bulky and heavy to meet the alignment requirements.